text:
Why didn't Boeing or Douglas make a jet airliner before the British DH Comet?
I was looking at the history of commercial aircraft and was wondering why UK-based De Havilland was the first to produce a jet powered airliner (the DH 106 Comet) when the US had a much bigger civil aviation industry at the time, such as Boeing and Douglas? They only produced their Boeing 707 and DC-8 after the Comet was introduced.

In the 40s and early 50s, the US were not as advanced as the British in all things concerning jet engines. After all, the jet engine was invented in Europe, in Britain and in Germany.

The answer is totally self-evident, they were invented in the UK.  (As stated in another comment.)

The Soviets also had an advanced program, and as usual with Societ aircraft, they were not beset by safety problems.

A jet technology answer would need to be somewhat nuanced to account for the fact that the heavier B-47 flew a year and a half before the Comet.   While not exactly easy to fly, it somewhat suggests that the issue was more believing something was a good business idea, than being unable to do it.

So did Canada with the Avro  Canada Jetliner, at exactly the same time pretty much.  The Jetliner was complementary to the Comet, being a shorter range intercity airplane.  It made a sales tour of the US in 1950 and was a huge sensation.  Avro Canada was ordered to set the project aside for the  CF-100 All Weather Interceptor program during the early 50s so Avro Canada had to decline US airline interest resulting from its sales tour (and a bizarre Howard Hughes/TWA subplot) and the program never really got traction after that as the company went on to put all its resources into the Arrow supersonic interceptor program by the mid 50s.  Odd that the Jetliner had its legs cut out from under it by government politics (the Jetliner was initially designed to a state-owned Trans Canada Airlines specification, who later back out) and the Comet by a fatal design flaw, so in the end Boeing prevailed anyway.
The main reason for the US lag was that jet engines were considered by private US airlines to be too immature as a technology to be used for commercial travel in the late 40s, so there was little market interest in the US until an actual aircraft was demonstrated (one factor: first generation commercial turbojets with crude fuel controllers, like the Jetliner's RR Derwents, were very difficult to manage).  On the other hand, both the Comet and Jetliner were developed as products for state owned airlines (BOAC and Trans Canada Airlines) wanting to be bold, so they were ostensibly private ventures but with a "guaranteed" state buyer for at least initial production, providing a huge leg up.
There was no US equivalent in the private airline sector in the late 40s/early 50s, only the US military, where the 707 actually got its start.

I didn't realise that US airlines at the time were private whereas British and Canadian airlines were state-owned, which makes lots of sense now, thanks! However, is there any reason as to why there was this difference in the ownership of airlines by any chance?

Mostly cultural.  The only federally run government transportation system in the US is Amtrak, which was set up to provide coach travel as the rail companies bailed to go all-freight.  It's a money losing federal government expense basically, that exists for political reasons. State capitalism pretty much always ends up that way.  Trans Canada Airlines became Air Canada in the 60s, was privatized in the 80s and is now a publicly traded private company.

@JulianF. Incidentally, most of the European countries eventually ended up going with something closer to the U.S. model of ownership. BOAC - now British Airways, Air France, Lufthansa, etc. are all private companies now (though, IIRC, the French government does still own a minority stake in Air France/KLM. Delta owns more of it now than France does, though, IIRC.)

Actually I was surprised to learn that the French and German gov'ts now own only small minority stakes in Airbus.

While US airlines were private, they still were regulated 1938-1978. They could only fly routes, set schedules, and charge fares set by the CAB. The CAB would ensure the airlines remained financially healthy. In order to ensure private airlines could compete against state-owned carriers in international airlines, Pan Am held a de facto monopoly on foreign flights.

@user71659 True. Thank goodness all of that went away.

@JohnK that's part fiction though, the governments own a small stake directly but major holdings through the parent companies which they also (part) own.

@user71659: Pan Am and TWA.

The conventional wisdom at the time was that jet engines were too inefficient on fuel to be cost effective in commercial travel, especially over long distances. It was Geoffrey de Havilland who challenged this when he was on the Brabazon committee and championed the idea that a pure jet airliner should be on the list of required airliner types.
His motives aren't entirely clear - it could be that his experience with with the H-1/Goblin engine used in the Meteor and designed by his friend Frank Halford meant that he had a better understanding of the benefits jet engines could bring to airliners or you could take the cynical view that since he not only owned an aircraft design company but also had close ties to pretty much the only serious manufacturer of jet engines in Britain at the time (Halford Engines which would become de Havilland Engine company in 1943) that having a jet airliner on the list meant that his company would be essentially a dead certainty to get the contract. So he stood to make a great deal of money out the idea, he had certainly done well out of providing jet engines to the military and a jet-based passenger liner would be the way to ensure continued prosperity when the war came to an end.
As for why they "got there first" well there's lots of reasons - the British and the Germans had invented and patented turbojets first, American efforts didn't really start until GE built the W.1 (with the help of Whittle) and the early years of American jet power was all done using licensed British designs.
Secondly you're forgetting that at the time Boeing was primarily a military supplier, it wasn't until they developed the 707 that they had any significant presence in civil aviation. Douglas had grown rapidly during the War but found itself struggling after the WWII ended - the government orders stopped and they were left with a surplus of aircraft. Going into the jetliner business would have been very risky and very difficult for them at a time when they were struggling.

I understand exactly where you're coming from in terms of the conventional thoughts of the time regarding the inefficiency of jet engines, however I wasn't aware that Douglas were struggling after the war - I would've thought that the tremendous success of the DC-3/C-47 and even the DC-4 would've kept them afloat easily! Also, I'm unsure about your statement that Boeing was primarily a military supplier as they were definitely producing civil aircraft at the time, such as the 247 and the 377?

@JulianF. Boeing certainly had civilian products but it was a small part of what they did at the time, the 247 was retired before the war (and less than a hundred were built), the 307 production was halted by the war (they only made 10) and the 377 wasn't built until 1947 and wasn't exactly a resounding success. Between 1950 when that finished and the 407 in '56 they didn't make any commercial aircraft at all it was all Military

@motosubatsu, comparing numbers is difficult because many of the Boeing 247's competitors got adapted as military transports, but the pre-war civilian airliner market was small.  "Less than a hundred built" is a reasonably successful aircraft for the era.

@Mark Indeed the numbers aren't hugely relevant.. my main point was that the 247 had already been out of production for some time by the point we are talking about so isn't really an example of Boeing's civil aviation presence at the time of the Comet

"Experience with that (tailless DH.108) machine led to the adoption of a tail for the Comet".  Yes, indeed.  The DH.108 did have slats, and the similar X-4 had some degree of success opening its clamshells a bit, but swept wings and no tail was generally a bad idea.

@Julian I guess after the war, there were so many surplus DC-3s around, that the civilian market dried up, as there are plenty of surplus transports being used in commercial roles. It would be interesting if the UK and the US had some "division of labour" scheme going on, since I can't think of a british transport akin to the DC-3 that was produced in quantity. Maybe the brits had less need for extensive air transport?

Back in the late 1940‘s, Boeing made all of its money in military planes. It had huge success with the B-17 Flying Fortress and B-29 Superfortress. On the commercial side of their business, Boeing was a distant third to the sales to Lockheed and Douglas, the two leaders in commercial aviation at the time. Even with their military success, their commercial offering, the 307 Stratoliner could not compete and lost money. Commercial aviation was an area Boeing wanted to focus on to help offset times when military contracts ran dry. The problem was coming up with a plane that generated interest in the civilian market because Douglas and Lockheed had really fantastic planes. They would need to do something radical to compete.
While de Havilland was busy building the Comet, Boeing was building the all-metal, jet-powered B-47 Stratojet and B-52 Stratofortress bombers. The B-47 was actually in service before the Comet. Boeing tried to create a commercial version of the plane, which they presented as the Model 473-60C in 1950, but failed to generate any interest with the airlines.
Boeing knew for a certainty that the US Air Force would need a jet-powered tanker to refuel planes. They made the existing KC-97 tanker, which was piston-powered, as well as the B-52 and realized that the maximum air speed for the KC-97 was the minimum air speed for the B-52, which made in-air refueling hazardous. So it stuck with the concept of an all-metal jet-powered commercial plane they could market along with a jet-powered tanker. This eventually became the Boeing 707 and the KC-135 Stratotanker, which are fundamentally different, but were derived fromm a common prototype, the 367−80.
Douglas Aircraft had a commanding position in the commercial aviation market after World War II with the DC-3 and the DC-6. Unfortunately, it was in the same financial pinch Boeing was trying to avoid with the end of government aircraft orders after the war. This lead to laying off nearly 100,000 workers. Douglas had to scale back, but was in a great position filling orders for existing planes and felt no need to rush into anything new.
At Lockheed, things were going very well. Before World War II, it had a firm commitment from TWA to build the Constellation. When the war started, the existing plane became a military transport known as the C-69. After World War II, it introduced the plane to the civilian market and finished filling orders for TWA.
Sleek and powerful, the Constellation was fast, had the first widely available pressurized-cabin in the civil market, and was capable of transatlantic flight. At the end of World War II there truly was no plane that really match it and for the next 15 years, they sold over 800 variants of the Constellation. In fact, De Havilland based the layout of the cabin and the flight deck of the Comet on the Constellation to boost appeal.
In addition, Lockheed had a very healthy military business. It was building the P-80 Shooting Star, America’s first jet-powered fighter and later, the F-104 Starfighter. There was no shortage of amazing planes being produced by Lockheed in this era. It just didn't focus on a commercial jet-powered airliner.
Unfortunately for Lockheed, jet-powered planes by Boeing and Douglas started taking over routes formerly run by piston planes. Since Lockheed did not have a civilian jet, it left the market in 1961. It didn't make a civilian plane until the the introduction of the L-1011 Tristar in 1968.
The Comet was the first to the marketplace, but being first is not always a guarantee of success. As we know, Boeing managed to dominate the jet-powered commercial market for decades, based on the success of the 707. One of the contributing factors to its success was based on the failure of the Comet.
After a series of unexplained crashes, the entire Comet fleet was grounded in 1954, and didn't fly again in commercial service until 1958. During this time, Boeing was developing the 707. Many of the Comet design failures that emerged helped Boeing avoid the same issues. The 707 had its first flight in 1957 and entered service in October 1958. The loss of planes damaged the reputation of the Comet, the fact the 707 could fly farther and carry more passengers doomed the Comet. It simply could not compete.

For the same reason the Soviets put a satellite in space before the US -- someone will always be the first, and there's nothing anywhere that says it has to be the US.

Sure, I understand that someone has to be first, but looking at the situation after the war, with the US having a much larger presence in the civil aviation industry compared to Britain whose presence was almost nonexistent, it seems a bit strange that Britain beat the US to the jet age, doesn't it?

@JulianF. With Germany out of the running for obvious reasons that left only Whittle and Halford making any real headway in jet development, both British. It wasn't about presence in Civil aviation.. It was about the engineering of jet engines. Everyone was looking to repurpose the tech gains from wartime, one of Britain's was the aviation jet engine so its not strange at all really.

@JulianF. and that larger presence was one reason why new airliner designs were slower to take off in the US. There were so many discarded military transports in the US that were converted into civilian airliner and cargo aircraft there was no real need for new aircraft for quite a few years, whereas the European airlines were pretty much defunct after the war and needed all new aircraft to start up again, which weren't available cheaply in bulk.

@JulianF. I have no idea what you mean by "presence." The UK aviation industry did not have the production capacity afforded by the US industrial sector and the peace of mind that comes with distance from the war, but there was no shortage of engineering know-how. Nothing strange about that.

Because the national commitment to build the Comet, along with the Brabazon and several other speculative aircraft, was part of the British War Plan.  The goal was to win the economic postwar, and they threw everything at the wall to see what would stick.
Similarly, the Soviet and Canadian governments put a high priority on getting a jetliner in the air.
In all cases, that priority included money, and those governments planned all along to pass any project losses on to their taxpayers.
Whereas in the United States, aircraft design is largely driven by airline commitments, and that requires the approval of two groups of private Boards of Directors who are singularly concerned with the bottom line.


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What is the fuel consumption of an aircraft in a holding pattern?
I am doing a research about fuel cost when an aircraft is about to land. they may be asked to be hold due to the traffic congestion at the runway. consequently they consume extra fuel. My question is how I can estimate the cost per minute or second being late of their *target time. Where can I get more details on this?
*target time: As I noticed each aircraft has a target time to land which is the most economical time and speed for them.
My research is about aircraft landing scheduling during rush hours where there are several objective functions such as maximizing the runway utilization, minimizing total delay and fuel consumption to be considered. these objective functions are subject to some constraints like aircraft's time window (earliest landing time,latest possible landing time), minimum time separation, Constraint position shifting...
In the literature that I have read so far they considered a fix fuel cost as a function of delay. as an instance: "Vj denotes the cost per unit time of the extra fuel associated with lateness relative to ULTj , then the overall extra fuel cost is : summation of Vj * (Landing times - ULTj) " (Aircraft Runway optimization, Mesgarpour, 2012)
Since it is more mathematically issue no body really pay attention to the details of that fuel cost or any other cost caused by the delay.

How are you "doing research" on a topic that you don't even seem to know the most basic info about?  Researchers are typically well informed and experienced in their field.

See also this example from Airbus: Getting to grips with fuel economy, $5.5 Holding.

@abelenky That's a little harsh, IMO, considering that we know nothing about the OP and what he's doing. For example, is it a professional project or a school one? And I'm fairly sure that not every researcher is "well informed and experienced", if only because everyone has to start somewhere. The same applies in every other job out there.

"How do I ask a good question?
We’d love to help you. To improve your chances of getting an answer, here are some tips:
Have you thoroughly searched for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers, and above all, it helps you get a more specific and relevant answer!"  [ask]

You guys may think i'm harsh, but I'm also the only one to have answered in the last hour.

Thank you for your feedback and the article. I am at the beginning of studying about that holding fuel cost. I edited the main question to mention where my question is originated from.

@abelenky that isn't the point, you directly chastised someone for asking a question that you determine to be "basic info",  just because they are a researcher...If you don't see a problem with that...Plus the fact that you did answer kind of contradicts your initial bewilderment.

@ablenky This is not a forum for sneering at people for asking questions about things they don't know about, or that you think are too basic.

@abelenky: Sneering at someone asking a question (in English the word 'research' does not imply an expert) and answering a question quicker than others are not mutually exclusive. I'm not sure what point you're trying to make here.

Every aircraft should have a published fuel-burn rate, typically measured in GPH (Gallons per Hour) or Pounds per Hour.
This rate does change a bit depending on ambient conditions (temperature & pressure), throttle, and weight.  But its a pretty good planning rate.
There are other costs, beyond fuel costs, associated with delayed landings, such as crew costs and running the airplane and engines closer to their next inspections and service times.

The fuel rate while holding depends on elements such as weight, altitude, speed and aircraft configuration.

Airbus uses the concept of green dot which is the speed with minimum fuel consumption per time unit in clean configuration.
This table shows fuel needs for a A330/A340 at 170 tons and 1,500 ft:

Fuel flow vs. speed. Source
While the green dot speed is the one offering the best fuel rate while holding, it assumes no flap and no slat. This speed may not be practical for certain airports where slats or flaps are advisable due to the rate of turn in the holding pattern.
To provide the necessary flexibility, Airbus publishes the fuel rate for three other combinations of speed/configuration (S speed is the minimum speed for flaps retraction):

Fuel flow vs. weight for 4 configurations. Source
Altitude is also a factor preventing an optimal fuel flow. Example for the green dot speed:

Percentage added when departing from the optimal altitude. Source
The total fuel required to hold can be somehow minimized by not flying at cruise speed when it is known that a hold will be required at some point. Savings can be done by flying at green dot speed to the holding point:

Source

That means determining the fuel flow depends on airline operating procedures and holding pattern design (e.g. altitude), but a maximum can be roughly predicted by looking at the manufacturer published documentation.

Why is GD different from the "min fuel" speed on that graph?

@pericynthion: That's right, the GD speed (maximum L/D ratio) is an approximation of the minimum fuel speed. But the difference in fuel consumption is really small. The GD speed is calculated for best climb gradient. Being already available it is also used for holding.

To answer based on some data I had correlating aircraft in confirmed holding patterns (not speed-restricted en-route delays) vs. high altitude cruise, the short answer was: they use more - mostly because they were in low-speed manouevring, with flaps set. I'd have to look at the data again to remember how much more, but I recall it was fairly significant: at least compared to cruise. This analysis was done as part of a study the airline was using to calculate the cost of capacity constraints in the terminal area.

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Did Airbus do anything about Qantas Flight 72?
I recently read about Qantas Flight 72
I'm wondering if Airbus did anything else besides release an Operators Information Telex? And I'm also wondering if this threat is still possible today? One last question, does the new Airbus A330-900neo and new Airbus A340 BLADE have the same ADIRU system as the other Airbus A330 and Airbus A340 or was something changed or fixed?

The ADIRUs presently used are totally different:
for exemple the hardware is of different generation bringing their physical dimension about twice smaller.
Todays AIRBUS used ADIRUs manage the GPS received data too. Internally the technical implementation of parameters is different, just due to technology evolution.
Most of these changes are not directly related to Qantas flight 72, but to new technology, for instance data interchange (such as sending the data of a label such as 224 as being the data of another label such as  204) due to a « bit » failure is not likely to happen nowadays as was the case in previous equipments because internally a « bit » failure is nowadays more precisely detected. Thus sending the altitude as being the AOA won’t happen today.

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Will manually removing nicks from compressor blades significantly affect the operation of the compressor?
I've recently found a channel on Youtube where a jet engine technician goes into great detail about the work he does on maintaining and repairing jet engines
In this particular video (and also an older prequel to it), he demonstrates removing nicks from compressor blade leading edges and subsequently smoothing out the leading edge. One thing that caught my attention was the tools he used: files and 100- and 400-grit sandpaper. He basically went over the leading edge by hand, removing a small amount of material in the process.
With the tools and the method, there is obviously no precision.
Is it actually acceptable to modify compressor blades that way? To what extent does it affect the operation and efficiency of the engine, if, say, some compressor blades are missing a millimetre off their chord, or have lost their twist by a few degrees?
I guess a related question is - what precision are compressor blades designed and built to?

Thanks to ymb1 for pointing out a related question, but I'm more interested in a quantification or analysis of the impact to the engine performance. It seems that the linked question explains the term blending (which is mentioned in the video as well), but did not go into details about performance impact.

He is a professional turbine tech and rebuilds jet engines for a living, so I suspect he knows what he is doing.

I never thought of this, but now I'm curious also. I've heard that the blades are carefully balanced by manufacturer, so eyeballing it seems to be a crude method that could lead to vibration, unless he's pulling it off and carefully weighing each blade that is sanded to make sure its within tolerance. Its probably not significant after one pass, but after several passes with the sand paper eventually the material removed could add up. I'm sure there are some A&Ps on here that can answer this. :)

I would agree with @Devil07 - even the nick itself could throw the compressor fan (or any other spinning engine component) out of balance, possibly setting up destructive vibrations. Again, there's an A&P somewhere who will come along and set us all straight.

@Devil07 you can find a bit on balance of the blades here

@zeta-band I don't doubt that he knows exactly what he's doing. He makes a point of emphasising that he's just a technician, but he definitely understands the principles and intricacies. I guess the more appropriate phrasing would have been, are compressors designed for such deviations in tolerances (assuming such deviations are even significant in the first place).

@Devil07 To add on to Dave's comment, the channel has some videos of the technician demonstrating and explaining compressor and turbine balancing. I expect they'll do balancing after doing stuff that could affect the balance, before they sign off on the repair or maintenance. The channel is a real treasure trove of information.

I think you'll find that the engine that that gentleman is working on is destined either for a stationary industrial plant installation; or less likely, a restoration of a privately-owned, single-pilot, vintage aircraft that will never carry passengers that will only run a few hours a year, if at all.
Having said that, these engines are still worth millions of dollars to their owners, and any outright asset risk, or even degradation in performance, is vastly expensive. If the operation was outside of manufacturers approved procedures, it wouldn't be taking place.

@zeta-band So said the salespeople pitching sub-prime mortgages. Never take confidence for knowledge.

@Agent_L given that they put the engines in the test cell and crank them up to full power, I think his techniques work just fine.

Yes, this is not only acceptable, it is required by the engine maintenance manual. The tools might be more sophisticated in other shops, but the basic concept of removing material by hand is the same.  The process is called "blending". The impact of sand or dirt on the blades causes little nicks and scratches. Those sharp or rough areas create what is known as a "stress concentration".  If left as-is, the nicks will eventually grow into cracks (metal fatigue). Smoothing out the nicks removes the stress concentration and prevents the crack from forming.  There is an impact on the performance/efficiency, but that's better than having your blades crack.  From my experience, the performance impact of what is shown in the video is actually quite small. As a rough guess I would say 0.01% - 0.1% efficiency loss. Much larger nicks can be successfully blended.
Edit:
Regarding how I came up with that efficiency number. Two thoughts:
First, The compressor shown in the video is a 10 stage compressor, and as a rough estimate, each stage probably has about 30 - 50 blades. I didn't try to count exactly but let's just call it 400 blades. It is a reasonable assumption that each blade does the same amount of work.  In reality some stages will be a little more heavily loaded than others, but it's fairly close. So if you removed 1 entire blade, as a rough order of magnitude estimate, you would expect that to be about 1/400 = 0.25% efficiency loss.  The amount of material removed is clearly much less than an entire blade, so the efficiency loss should be less than 0.25%.
Second, I have seen compressors that had much much larger nicks be blended out and have on the order of 0.1% - 1% efficiency loss.
So between the two of those ideas, I made an educated guess on the efficiency number. Could I be off by a little bit?  Absolutely. But I'm probably at least close.

Since you put forward a figure for the efficiency loss, may I ask how the figure came about? I have no idea how it might be quantified from real-world performance, but I imagine it would be possible to run CFD simulations and arrive at the relative degree of compressor pressure loss, for example.

The process normally used to alter the shape / remove material is called linishing and it is used in both manufacturing and maintenance but do not attempt it yourself! Only a professional should even consider hand linishing a blade.
The shape is typically controlled to within at least 0.1 mm* during manufacturing, though it can be even lower. There some highly experienced people who can actually achieve this level of accuracy, but more commonly robots are used to get a more consistent shape and the shape is verified by measurement machines after, something I'd be surprised if the person in your linked video did.
If you distorted the shape of the leading edge too much from the intended design it can have a significant effect on the performance as it can cause early flow separation making the blade less efficient. There is also the effect off stress caused by notches on aerofoils to consider.
While of course an off design shape is probably better than the flat/distorted shape from a notch, it is still a job for a professional. Your life literally depends on that engine working properly and it would cost a fortune to replace if you messed up. So why would you want an amateur maintaining a critical component?
As for any efficiency loss, that is a something we could only guess at without some data from an engine manufacturer to back it up, therefore it would be quite meaningless.

*To give you an idea of the accuracy achieved during manufacturing, here is an example of a GE machine that verifies blade shape. It has a published accuracy of 0.001", which isn't bad but there are machines capable of a fifth of that. You typically want your machine accuracy to be 10 times better than than the accuracy of what you're trying to measure.

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text:
Why airliners fly so high even when winds are more suitable at a lower altitude?
While playing a flight sim, I noticed West winds were very strong at levels >FL350 and weaker around FL270 above the US.
I took a look at Flight Radar 24 to see at which level actual airliners were flying, and I was surprised to see they're mostly over FL350, despite the lower ground speed and increased fuel burn I assume should occur
Is there any reason for that ?
FL270 :

FL390 :

Related, if not answering the question: http://aviation.stackexchange.com/questions/12541/why-are-many-jet-aircraft-designed-to-cruise-around-fl350-370

these answers are really interesting but they don't mention winds

I think there is enough difference to not be a dupe if the focus is on why they don't fly at this height for these conditions rather than why they're generally designed to fly at a given height. The answer being that  they're designed to fly at FL350 and the detrimental effect of flying in off-design conditions is bigger than the gain from favourable winds.

@fooot that's much more like it!

indeed ! thank you @fooot !


text:
How can I calculate a pitch/power table?

I want to make a pitch and power table for C172s based on calculation, just like I attached above.
I picked up this table on internet, but I'm not sure where it comes from.
Do you have any ideas how to get these values?

I don't completely understand your question. In the example you included, which columns do you want to calculate? What values do you intend to use as input to the calculations?

Well, let's say we want to fly C172S in cruise level flight, 100KT. In that case, the values, pitch and power, will be only one in theory, right?
My question is how to get these values, pitch and power, based on calculations.

I got the answer from cessna company, as below.

The pitch/power table you have provided is not a product of Textron Aviation and has been developed outside of our flight testing and engineering. We have no formula available for calculating required pitch attitudes, The table shown appears to be developed by a flight school based on actual flight test observations.
In general terms, pitch relates to angle of attack. Angle of attack required for certain climb and descent rates are dependent on variables such as gross weight, C.G. location and indicated airspeed. In relation to the quote “pitch + power = performance”, a more accurate approach for developing a quick reference chart assuming the aircraft gross weight and C.G. remains constant is to match indicated airspeed with power settings. Pitch + power can approximate an airspeed, but more accurately power + airspeed = pitch. Flying an aircraft “by the numbers” relies on power settings and airspeeds, which consequently will produce a certain pitch attitude. Conversely, to facilitate a desired climb or descent rate we set power and approximate a pitch attitude to arrive at the desired airspeed.
The interrelation between pitch and airspeed is for the most part interchangeable, but most accurate is thinking of pitch attitude being a consequential product of power and airspeed in the context of normal flight maneuvers.

Well, nothing new here. But I found that there are no exact formula to deal with power and pitch table. I'll try to collect actual data.
Thank you guys.

When you are flying you will be looking at airspeed. Pitch, throttle setting (and trim) will depend on this and whether you are climbing, descending, or in level flight.  Data can be gained from experience, or one can go on a flight dedicated to gathering this information all at once.  Fill in the blanks one at a time!
A chart such as this could be a useful part of the POH  in the event of an emergency, such a malfunction of the airspeed indicator.
A scenario pointed out in comments would be a pitot tube icing event. Rpm settings for pitch would be useful for maintaining straight and level flight, giving valuable time for problem solving. Possible solutions mentioned were use of GPS to get ground speed, then land into the wind so airspeed at least is as much or more than ground speed. Also on the list would be to ask ground radar for your speed and fly a straight in landing pattern factoring in the wind.
But under normal conditions, your eyes belong either out the window or on your instruments.

I disagree. The knowledge contained in table is important e.g. as a tool to cross check airspeed indicator. Pilots should have at the very least a rough feel for which pitch & power combinations are normal, preferably even by flight phase, and which are not. In the absence of aerodynamic and propulsive calculation model, I would probably try to fly the aircraft, trim meticulously and take notes in various flight phases, maybe from a couple of different flights, in order to build the table from real aircraft data. Cross validate with a sister ship, if possible at all.

Yes sir, anything that helps familiarize one with the operation of any machine is helpful.  I just did not think it was practical to be reading such things while flying.  I would be more on full throttle and Vy on climb out, controlling speed with elevator.  And flying with a good instructor helps too!

BTW, trimming meticulously and taking notes (as a retired researcher) would certainly impress me, particularly in the testing and development stages.  This data would be useful in writing the POH.

Agreed. This should probably be memory item rather than having to rummage through the POH for it while trying to not lose control with the other hand while encountering pitot icing in IMC.

That is a great point, as reliability of airspeed indicators is critical.  These days, I wonder if GPS can tell?  Kudos to those who must fly in all weather.

One would have to add or subtract wind to get airspeed.  Coming in to land in a headwind, the airspeed would be equal or greater than the ground speed.  I hope the run way is not icy too!

Unfortunately you can’t derive wind speed with on board measurements or calculations without knowing airspeed...

Well, that is why I would land into the wind, with GPS or ground radar one would be going at least as fast as ground speed.   So now we have more than one way to solve.

True. More difficult once at greater heights/distances from an airfield, though.

Thank you guys for nice discussion. I just tried to ask cessna company via email. I'll post update here once I got response from them.

"Unfortunately you can’t derive wind speed with on board measurements or calculations without knowing airspeed"-- you can if you are willing to change heading.Here's something I've often done while flying a hang glider w/ no airspeed indicator-- carefully observe what heading gives lowest groundspeed while flying wings-level at trim airspeed.Then do a quick check of the groundspeed on the reciprocal heading by turning to that heading and rolling to wings-level.The bank angle as you approach the target heading should be shallow enough that the airspeed is stable by the time you are wings-level.

The difference between the two groundspeed readings is equal to twice the windspeed. PS the reason for taking the most time with the upwind reading is that you normally don't want to spend a lot of time flying downwind in the context of local ridge-soaring or thermal-soaring in a low-speed aircraft.  If your destination is in fact in the downwind direction, you could reverse the procedure to minimize the detour from your intended course-- it would work just as well either way.


text:
Does international mail go in passenger planes?
I have a shipment from Canada to South America coming, and it's curious that the "priority" FedEx option takes 6 days to arrive, when there are daily flights between the two destinations.
So I'm assuming mail does not go in airliners.
Am I right, and if so, what's the reason for that? It seems it would be extremely more efficient at least for small shipments.

Companys like FedEx are having their own aircraft, so why would you occupy space in a cargo room in a civilian aircraft which would normally be reserved for passenger cargo

Just to clarify: "civilian aircraft"? As opposed to a military or government aircraft? I assume you mean "an airliner"? But, if you're contracting FedEx to make the delivery, they're going to fly it on their own routes, not whatever "daily flight" you're looking at in the airline world. FedEx is going to move it to their closest hub, and then possibly another hub (or even two) prior to delivery to the destination city.

@HugoWoesthuis Actually, both the USPS and FedEx make use of passenger aircraft for mail and cargo for the simple reason that it's a source of revenue for the the airline. See http://science.howstuffworks.com/transport/flight/modern/air-freight1.htm. Also, back before my retirement in 1999, you could bring packages to the airline I worked for to be put on a particular flight and then held for pick up at the destination. I don't know if this practice was continued after 9-11-2001.

I did mean airliner, looking really stupid now :)

@Terry thanks for the tip (didn't know it)

So I'm assuming mail does not go in civilian aircraft.

Like many thing in aviation it depends. For shipping it will depend on where you are shipping to and from, how big the item is and the chose method of shipment. Both FedEx and UPS (who are private shipping carriers) operate large fleets of cargo airplanes. In many cases a shipment may end up on one of their own cargo planes. However their planes, like passenger planes run routes that may be pre-decided. As such passenger airlines sell the leftover cargo space to anyone willing to buy it. You can find a nice blog post on how it works here. UPS/FedEx may pre-broker a deal to buy a certain amount of cargo space per year from an airline to obtain a better rate or they may buy it on demand as needed.
Now Air Mail is a bit different as its offered (here in the US) by the government postal service. Technically the USPS no longer offer airmail service as it was once called but does still offer domestic and foreign guaranteed time shipping. All of these items are moved in cargo space on Commercial Passenger Planes or by under contract by FedEx as the USPS no longer operates any aircraft.

Am I right, and if so, what's the reason for that? It seems it would
  be extremely more efficient at least for small shipments.

Like most things in aviation low cost will always beat out marginal efficiency. If FedEx can ship a package at a significantly reduced rate but in turn it will take an extra day or two to arrive than many customers will see a value add in that. In the same vein it would be very efficient to fly every passenger in a small plane to an airport closer to their final destination and have the plane depart when the passenger needs to, however the cost of that simply would never work out.

"The U.S. Postal Service alone leases space on 15,000 of the approximately 25,000 scheduled passenger flights each day. Commercial airlines make about 5 to 10 percent of their revenue from hauling freight." ... would have saved a heck of a lot of typing :p

FedEx and other express shippers likely have contracts with commercial carriers.  The six day shipping time tells me that they could only secure reliable,  affordable rates with a 6D service level.  Sure, you could probably 2-day it but the costs to FedEx will probably push the price you pay through the roof.  Would you pay 3x to 4x what you paid for your six day service for a two day service?

Also, don't forget customs processing. This takes easily two more days.

I have had an item arrive in 2 days from the US to the UK. I didn't pay the shipping but shipping costs was in the hundreds for a pretty small replacement for one of our IBM servers. No idea how it got through customs so fast, maybe they have priority customs checks for such customers? But saying that I've had chocolates and perishables sent from US to UK and they always arrive, which means nobody has checked the contents or ran it through an xray machine.

Freight shippers have mechanisms in place to speed the customs process along.  Your shipment was probably place on a pallet of parcels simply because the guy packing it had space and your package was within reach.  That pallet was expedited through customs on a higher service level and your box got delivered early.  When I flew express Next-Day, we would routinely load the plane with 2 day and 3 day once the Next-Day stuff was on board.


text:
How does FlightAware correlate flights to Part 91 flight plan data?
I'm looking at some flights in FlightAware. With the scheduled air carrier flights, their call-sign can be crossreferenced with a flight schedule database to determine the origin and destination. How are they populating the origin and destination fields on small Part 91 IFR flights being conducted by a Cessna 172?
Do they have some sort of access to the Aeronautical Message Handling System (AMHS) or Aeronautical Fixed Telecommunications Network (AFTN). If not, how else could they be receiving this data?
In reference to the possible duplicate question, it's unclear to me if the term "flight data" in the context of that thread is in reference to the near real-time (NRT) flight track flight data, or a more robust data set which includes the details of a flight's route,  as filed and/or cleared.
Normally that type of flight plan routing data is transmitted over the AFTN/AMHS. It would be very very interesting if the FAA is integrating AMHS flight plan FAA data into the ADS-B/SSR flight track data.
Whilst I doubt know for sure, I’m relatively certain the flight plan routing data is integrated with track data by air traffic management (ATM) system and available to ATC personnel. What I need a better understanding of is how and at what point that integration occurs.
Is it an automated process occurring upstream or is it entered manually by the ATC personnel? If it's automated then is it AFTN/AMHS data or another source? If FlightAware is receiving this data, is it included as a single feed our do they have a separate feed? If the flight is scheduled, assuming the majority of origin/destination information results from callsign/ flight schedule cross-referencing, if either sources routing information conflicts with the other, which has primacy?
I concur that I understand the 5 minute FAA track feed delay was eliminated, but I don’t have a source to confirm.

Possible duplicate of this thread.  The FAA publishes all IFR data in real time (to industry need-to-know companies called "tier one"), and "tier two" businesses like FlightAware can purchase this same data at a 5-minute-delay-output.

@Jimmy I believe that time delay is now omitted.

My understanding is that the FAA publishes these data via the System-Wide Information Management (SWIM) suite, specifically the SWIM Flight Data Publication Service (SFDPS) and the SWIM Terminal Data Distribution System (STDDS).

SFDPS allows consumers to receive real-time data for analytics, business processes, research, and other activities. ...
SFDPS provides consumers with access to National Airspace System (NAS) en route information by providing the following services:

En Route Flight Data Publication & Query

This information is collected and disseminated automatically; individual controllers have the responsibility of ensuring flights are marked as "departed" if the radar system does not automatically recognize them as having departed, but that is the extent of any human interaction required.

The data that FlightAware first receives for most commercial flights
  is sometimes delivered a year in advance via schedules published by
  the airlines. That data then usually remains unchanged until a few
  hours before the flight. Pilots or air traffic control operators
  controlling airspace on the route of flight will push out new data
  with a flight plan that provides specific details about the planned
  routing, altitude, and speed of the plane. But that’s where the static
  data end and the real-time data begin.
“When the door is shut and the parking brake is released by the
  pilots, the aircraft or airline will send us an ‘out’ message that
  indicates it’s pushed back from the gate, and we know that departure
  is imminent,” says FlightAware’s Baker. “As soon as the weight is
  lifted off the landing gear, we often get an ‘off’ message from the
  airlines or the aircraft itself that indicates the plane is airborne
  or a departure notice from air traffic control.”
Once en route, FlightAware continues to get position updates from the
  plane via radar installations at air traffic control centers and via
  ADS-B, along with continued updates on the plane’s route from air
  traffic control. All of this information is then fused together by
  FlightAware’s software, which uses it to determine the plane’s
  estimated time of arrival, and then displays the aggregate data for
  the flight on its website and in its apps.
“We detect the landing either by seeing the plane slow down below
  flying speed, by getting an ‘on’ message from the airplane, or by
  receiving an arrival notice from air traffic control. From there, we
  may have surface coverage to track the taxiing on the ground, and
  eventually receive the ‘in’ message from the airline indicating it’s
  safely parked at the gate,” says Baker.
Now multiply all the above steps by the thousands, or one for each
  plane in the sky across the world at any given time, and you’ll begin
  to appreciate the amount of data that fight tracking websites’ servers
  and algorithms are crunching each and every second.
https://www.fastcompany.com/3044490/how-flight-tracking-apps-work

Welcome! SE doesn't work this way, you cannot only copy-paste. This is possible, but only to illustrate your own answer (and the source must be cited).

Well, it answers the question so why retype it? I added the link...

While the answer may be in there you could format it much better and explain/highlight the most relevant parts.

I'll try and do that next time, thanks for the heads up

This does not actually answer the question, because this talks about receiving something “from the airline”, which may work for “part 121” (airline) and “part 135” (commuter and on-demand) operations, but there is no “airline” in “part 91” operation, i.e. general aviation.

They don't have the flighplan data but can calculate dep and dest by ads-b positions. It's fairly easy...

Your last comment answers the question.  Your borrowed "answer" does not.


text:
Why is the available power in propeller engine is almost constant for every velocity?
I surfed on the internet for an answer but I didn't find any. I'm taking Aircraft Performance course. I saw that available power for propeller engine is almost constant for every velocity.  But I don't know why...

I added a graph showing it

Why do you not expect it to  be more or less constant?  It will help people to  answer.

Because the propellor blades have variable incidence and operate at constant rotational speed. As the plane picks up speed, the propellor blade angle is adjusted so that the local angle of attack stays the same.

This is only true for variable pitch propellers which are not found on all prop planes.

@Dave is correct, but ALSO incidence will change with the aircraft angle of attack, and that will affect P factor, and reduce efficiency. However, incidence is a tertiary factor for aircraft power.

@ Mongo Yes Dave is correct, variable pitch propellors are only found on aircraft with variable pitch propellors. In the bit of airspeed that the OP shows, power curves are pretty flat. Helicopter manufacturers would disagree with incidence being a tertiary factor for power: the collective is what applies power via incidence change, and the fuel governor keeps the rpm constant.

@Koyovis the OP asked within the context of what appears to be an airplane. I agree that in rotorcraft pitch is a primary factor in power availability, and that incidence is of greater consequence than in a conventional airplane.  However, the curve provided by the OP is consistent with airplanes, and in that context incidence is tertiary. As a point of clarification, in airplanes, prop incidence is a function of mounting of the engine, and the AOA.  In rotorcraft it has slightly different usage, and rotor incidence often refers to pitch of the rotor relative to the hub.

It is a gross simplification, assuming a constant speed prop.  If a fixed pitch prop, it is non-linear.  Even with a constant speed prop it is not exactly linear.
Lesser factors for power available are the angle of attack/angle of incidence, which will change with airspeed, assuming level flight.  Ram air is also a minor factor on some engines.
The diagram you show is a simplification meant to show you that the power is the same, regardless of airspeed, but in reality it varies.  How much? I can't say for certain in general, but on one aircraft I collected data on, I recall it varying about 6% in the 20 knot window we were looking at.  And to be clear, that was power converted to thrust, not simply power plant power.

available power for propeller engine is almost constant for every
  velocity

This is because full power is always, in theory, available to you no matter the velocity of the aircraft. In other words, you can always slam the throttle full forward.
The required power is the power that you would need to move at a given velocity (through the air). When the required power equals the available power you would hit your maximum velocity. Above the available power limit when the power required to go a given velocity exceeds the power available from the engine you would not be able to go that velocity (with the exception perhaps of in a dive).

While these statements may generally be true, they do not address why the available power in the chart is almost constant.  But to a finer point, the engine prop/engine transfer efficiency is less in a propeller when the plane is stationary.  As the plane moves, the prop efficiency increases. Therefore, the power produced also increases.


text:
Advice on making a jet engine
I'm a software engineer and recently want to make a jet engine myself. Since I am a newbie in this period, I want to know what basic knowledge is needed for making the engine. I wish to use it on my radio control aircraft, which has a 1.6m wing-span.
Hope someone can give some advice. Really appreciate.

Lets use an analogy. If a hobbyist software engineer came to you and said "I want to design a search system on par with Google, and just as fast" what would your advice be? (hint: walk before you run). Perhaps start with looking at designs for other scale-model engines before diving in yourself. See what improvements you could make to existing designs.

"I want to make a perfect one as much as possible..."    Does that stand in contrast to the early jet-engine designers, with decades of engineering experience, whom you seem to suppose must have set their standards lower?  Do you think that early jet engines exploded because the engineers who designed them thought that was okay and didn't aspire to "a perfect one as much as possible"?

You can find instructions and plans on the internet for making your own pulsejet engine. Like this one from Popular Mechanics

Well you'll need to know machining (use of end mills, lathes,  welding, etc), structural mechanical design (statics, dynamics, strength of materials, bearings, machine elements), heat transfer, thermodynamics, and control systems. It's a lot for a beginner. I'd recommend starting with something easier. For example, design and build a small robot to vacuum your floor. Or design and build a radio controlled car or boat from scratch. Any type of project like this will be challenging and help you learn what you need for a bigger project.

Ok, Although it seems hard to begin, but I'm sure I will study them in my spare time. Thanks a lot.


text:
How was the lost F35 from the Queen Elizabeth recovered?
In 2021, an F35 Lightning II from the Royal Navy carrier Queen Elizabeth crashed into the sea on take-off.
It was later reported that the aircraft was recovered from a mile below the Mediterranean.
Has there been any further public information about how the aircraft was recovered,  what equipment was used, and whether the whole aircraft was raised or just the sensitive equipment that they carry?

The recovery was likely done the same way the other F-35 in the South China sea was recovered. There are pictures of the recovered aircraft here: https://theaviationist.com/2022/01/21/photo-recovered-f-35b-wreckage/

The aircraft blackbox on most US navy aircraft have a transponder that shows a general location.

The report on the incident came out last year, it has detailed information on the full event and shows the recovery process in detail.

Shortly after impacting the sea BK-18 sank in approximately
2,000m of water. A UK led salvage operation was conducted using chartered
vessels. The aircraft was discovered, by remotely operated vehicle, inverted
on the seabed, intact with a few minor parts such as the ejection seat
detached but close to the airframe. The salvage operation recovered the
aircraft, as well as all of the detached items and then transported them back
to the UK. The CSMU had a sonar locator beacon to assist with recovery of
the flight data recorder in the event of loss in water. The beacon was not
detected during the search and recovery.

Full report can be found here
So to your question,

what equipment was used, and whether the whole aircraft was raised or just the sensitive equipment that they carry?

They recovered the full aircraft.

Thanks! It looks like the specifics of the salvage process are classified and unlikely to be published in full, but that report gives lots of other interesting details.


text:
What is the difference between Tilt-rotor aircraft and Tilt-wing aircraft?
I've  heard more about tilt-rotor aircraft like the Bell Boeing V-22 Osprey
more than a tilt-wing aircraft like the XC-142
What are the differences (other than one changing the degree of wing or rotor), pros and cons of the two?

I can see that it would have a difficulty in holding a position in a windy condition.

I would say that the complexities of tilting the entire wing are what compelled Bell to choose just the nacelles.
By complexities, I am thinking 2 major systems. The first is the flights controls. Based on the how old that image looks, I suspect that aircraft want designed with a fly-by-wire flight controls system if it was even an option. That would be, in my head, the only simple way of managing the flight control sister's. Otherwise the designers would need to get VERY creative with the pushrods or cables & pulley systems. That would be an engineering nightmare!
The other system would be fuel. Engineers are going want to put fuel in the wings, as opposed to under the floor in the fuselage. That way cargo space is not used, bit more importantly, that much weight centered on the shortest works reduce the ability of the aircraft top perform missions for to the Zero Fuel Weight considerations.
Again a tilting wing creates some engineering challenges they may just want to avoid. The wing tanks would shift weight as they tilted back, and they would need to ensure fuel could still get to the engines. That's not even the hard part either. Think about trying to run the cross-feed lines through a rotating wing root! No thanks!!
Hope that helps, that's all I've got!!

Could the p phrasing be improved? Not easy to follow now.

Yeah, I'll look at it later, I was exhausted when I wrote it!!

In the case of those two particular aircraft: V-22 and XC142, the big difference is not in the fact that the engine nacelles rotate versus the entire wig, it is in the complexity of the propulsion design.
The XC142 has conventional engines and props that rotate with the entire wing.
The V-22 does not have conventional propellers. It has two cyclic pitch control helicopter rotors.
Why the more complex helicopter rotor design was chosen over the simpler aircraft style propeller design is an interesting question, one I don't fully understand myself.
On the surface, cyclic pitch vs simple pitch will give a much greater degree of control during hover, and a greater latitude in dealing with less than perfect CG issues, but I'm sure the reasons run much deeper than that.


text:
Could low pressure compressor blades be made of aluminum?
With the compressor blades on a gas turbine, could the low pressure blades be made of aluminum, or would it be catastrophic?
Edit:
Like the 6061 alloy.

Why would you want to?

If your turbine operates on steam or compressed air then I think it's feasible. But if you mean hot combustion gas at 1000+K temperature, then it would be very very hard.

You should be more specific. Which gas turbine?

@ManuH any? It's kind of a generalized qeustion

@Lilrags16 You may precise it in the question, and there is a chance the question will be closed as too broad.

The answer is yes, and they have been, in the early days. The blade speed is lower than can be reached using titanium or steel, so more stages are required.


text:
Why do many ram air inlets have this shape?
I often see this particular shape for ram air inlets.
Here on an older 737

It's stretched on the newer 737's but still the same basic shape

A also see it a lot on cars.
1979 Camaro Z28

Lamborghini Countach

Is there some aerodynamic advantage to this shape, and if so why?

Note that the inlets on many cars are purely cosmetic.

@RussellBorogove As is probably the case with the Camaro. I always assumed it was intended to imitate the appearance of an aircraft inlet. But that's probably not the case with the Lamborghini!

@RussellBorogove on the camaro it feeds the engine air intake, the lambo uses it to cool the brakes.

I was just saying that the shape of the Camaro hood scoop is probably that shape for cosmetic reasons whereas the brake cooling duct on the Lambo is probably much more carefully engineered for aerodynamics.

related: http://aviation.stackexchange.com/questions/16566/what-exactly-is-this-opening-in-the-belly-of-a-boeing-737

Those are called NACA inlets or NACA ducts. As wikipedia mentions:

When properly implemented, a NACA duct allows air to flow into an internal duct, often for cooling purposes, with a minimal disturbance to the flow.

So yes, there is an aerodynamic advantage.
As for the "why", if you're in the mood, you can have a detailed look at the original report (I'm not able to properly summarize it).

This specific inlet type is called a "NACA inlet", "NACA scoop" or "NACA duct", since it had been invented by Francis Melvin Rogallo at NACA in 1941 (PDF) and refined by scientists at NACA (now NASA) Ames. Its main advantage is its simplicity: It just needs a properly shaped cutout in the skin and a rounded rear edge, whereas the airscoops it replaces need carefully shaped contours.
The working principle is quite similar to that of a delta wing, only in this case the actual wing is missing, and is surrounded by sheet metal. But like on the swept leading edge of a delta wing, the swept left and right edges create a vortex which is swallowed by the actual intake at the rear of the cutout. This helps to create a lot of flow for the given area, even though efficiency is below that of a well-shaped airscoop.
The moveable flap in the middle of the cutout is for deflecting some of the air if less than maximum airflow is desired. This item is easy to manufacture, but reduces the efficiency of this type of inlet further.


text:
Why can US deny airspace to commercial flights?
On September 25, 2011 i flew from Mexico City (MMMX) to Frankfurt, Germany (EDDF).
It was a comfortable night flight in a Boeing 747 until we started to fly over the Gulf of Mexico in holding pattern.
After some time, the passengers started to ask what was happening and the cabin crew told, that everything was fine.
After more time the flight crew told, that the United States airspace was denied to our flight and that the crew was doing everything possible to arrive to Frankfurt on time, including the request of permission to Lufthansa central for changing the route adding a refueling stop somewhere.
We threw 18 tons of fuel over the Gulf of Mexico and returned to Mexico City airport.
Mexican federal police entered to the cabin and peacefully took some passengers out.
The airplane was quickly refueled and because the long runway was under a routine maintenance, we had to wait a lot inside the plane.
People got crazy, some passengers were worried about losing connections with other airlines. On the second attempt the airspace was granted and landed in Frankfurt with around 4 hours delay.
Why can US deny airspace to commercial flights?

Related, maybe even a dupe

Every country regulates its airspace. You will find the ones for the US airspace on the FAA website.
https://www.faa.gov/air_traffic/publications/us_restrictions/airspace/
What went wrong is speculation, but most probably had to do with Advance Passenger Information System (APIS). When filing a flightplan the passenger list is transmitted and the request for overflight was obviously denied.

Overflight privileges are part of what is known as freedoms of the air. In this case it would be the 1st freedom of the air, which is overflight without landing. These freedoms are negotiated between nations by treaties. In this case it would be a treaty with Germany, since it was a German airline. It's most likely a treaty with the EU, which Germany is part of.
I don't know the specifics of the treaty with the EU, but they certainly have 3rd and 4th freedoms. I can't imagine they wouldn't have 1st freedom rights. I'm sure aircraft have to meet certain requirements, but that wouldn't likely be the problem. The treaties will also allow for each country to ban specific flights or airlines. This often happens when an airline has numerous safety violations, but once again, it was Lufthansa, so that's not likely either. There are probably stipulations in the treaty as to certain passengers for security risks, etc. Since they removed passengers it obviously had something to do with those specific passengers. They may have been on a US no fly list or something. No way to tell.

By the Convention of Chicago, each ICAO member State
A. Is sovereign for its airspace, in accordance with article 1:

The contracting States recognize that every State has a complete and
  exclusive sovereignty over the airspace above its territory.

B. Has the possibility to limit its airspace access to commercial aviation in any way deemed necessary, in accordance with article 9 (b):

Each contracting State reserves also the right, in exceptional
  circumstances or during a period of emergency, or in the interest of
  public safety, and with immediate effect, temporarily to restrict or
  prohibit flying over the whole or any part of its territory, on
  condition that such restriction or prohibition shall be applicable
  without distinction of nationality to aircraft of all other States.

This convention was signed in 1944 and, with its 19 annexes, is the base for commercial aviation all over the world.
See more on Wikipedia: Chicago Convention on International Civil Aviation

Obviously the "removed passengers" were on some kind of US "no-fly" list at a bare minimum.  Possibly they might have been on some US "wanted" list, who knows?  All nations retain the right to say who can and who can't fly through their airspace.  Nothing new here.  Next time the Mexicans will probably be a bit more careful about who they let fly through US airspace, obviously.

It seems unlikely that it's because some of the passengers were wanted in the US. If that was the case, the US would be delighted if the plane overflew them and had to make an unscheduled landing on US soil.

I'm curious why the US would care about someone on an overflight being on a no-fly list so long as they didn't land in the US - if they're worried about hijackers, they should note that it's just as possible for a plane to be hijacked outside the US and then flown into it.


text:
What airplane model does this toy fighter jet represent?

I couldn't figure out what this plane could be, I was thinking of a Eurofighter Typhoon but then I realised that the Typhoon has only one vertical stabilizer.

These sort of toys are often based on,  but not exactly the same as,  real models.

BTW the white -2 is a Shenyang J-35. The single-engine one next to it is F35. The small black one on the far side is MIG-29. All of these models changed the V tail to conventional straight tail probably because V tail won't come out of injection molding.

Your "EJECTION PLANE 22-3" most closely resembles a Chengdu J-20. Its proportions are more or less correct, and has the distinctive forward-sweep of the air intakes.
The tailplanes need to be canted outwards, and the nose a little pointier (problematic on a child's toy); otherwise it's a fair approximation.

source
(Both the Typhoon and the J-20 are two-engined aircraft, which you can tell by the two nozzles at the rear of both types.)

Typhoon does have two engines (or at least exhaust ducts), but only one vertical stabilizer.


text:
What (if any) is the fastest way to make money with a pilot's license (without being full time employed)?
I'm in the USA, and I was considering getting a pilots license with the idea that I could have like a small charter plane and make some money.
However, I learned that after getting the 'initial' license, it's prohibited to charge anyone for a flight. I've heard that pilots can sometimes do contract work teaching others to fly, but I'm not sure even that can be done with the first license people can obtain.
I'm not sure of the license expense that is required to be able to charter a small plane for someone, but maybe that's the only way to see any ROI on a pilot's license?
Is there any way to make any money without becoming a W2 pilot for some airline, or is being a pilot mostly just an expensive hobby unless you have fulltime pilot career aspirations?

I deleted the "passenger" tag and added "FAA Regulations" because I thought it was more appropriate, and you can't have more than 5.  Roll it back if you disagree.

You can start a one-man charter service, but the hoops you have to jump through, and the expense, might take quite a while just to make your money back. Prolly the easiest route would be to get an instructor's rating and just freelance, but you have to really like teaching.

This question reminds me of the old adage: Q: How do you make a small fortune running an airline? A: Start with a large fortune.

@GregHewgill That applies to most things in life, not just airlines...

I want to answer "drug running" but I also don't want to be banned...

There might be a niche in transporting high value or urgently needed (non-human) items from place to place. An assembly line that is down costs big bucks every hour, not to mention things like rare drugs and freshly harvested organs.

I feel like a lot of these comments were definitely "worthy" of being answers that could have given everyone the up-vote-swag-points they deserved. :) The idea of a private carrier for goods / logistics sounds extremely interesting.

To answer your first question, there are five types of pilot certificate:

A Student Pilot certificate is the very first type of certificate you will get while you're learning to fly. With this type, you can't be compensated for flying, you can't carry passengers at all (regardless of if they're paying or not), and you must have your instructor's blessing to fly solo.

A Recreational Pilot certificate is the cheapest and easiest to obtain of the "real" (for lack of a better term) pilot certificates. With this certificate, you're limited to only flying certain aircraft, can't fly at night, can't be compensated for flying or use your plane for business, and are limited in where and how far you can fly.

A Private Pilot certificate removes a lot of the restrictions of the recreational cert. You're no longer restricted in where you can fly*, the number of passengers you can carry, can fly at night, and are even allowed some (very limited) business use. You still can't be compensated for being a pilot, though.

A Commercial Pilot certificate allows you to work as a pilot, and fly for compensation or hire.

An Airline Transport Pilot certificate allows you to fly as a captain on the big airlines.

To answer your second question, the costs associated with owning and operating your own charter company (insurance, licensing, airplane upkeep, etc.) means that doing so part-time will make it very difficult (though not impossible) to make your initial investment back. If you just want to make a little money by occasionally flying, your best bet is to get a part-time position at an existing charter company (and even then, it's going to be quite a while for you to make back the money you spent getting your commercial cert).
*Obviously, there are still some restrictions on where you can fly, but they apply to everyone and aren't based on the license you hold.

The money to be made with a fairly new Commercial certificate is limited by the fact that those jobs are in demand from many other pilots with similarly new Commercial certs who are seeking to build their hours and move up the ladder toward an airline job.  Much of the total compensation of those jobs is the time itself, and the pay isn't great.  The jobs get filled in expectation that the "big bucks" come later, and the low pay gets endured with the future goal in sight.  Without that goal, the pay alone often won't look very attractive.

Yea, I'm not looking for the big bucks necessarily. Just a potential small business or  side-hustle opportunity to be able to make back the 10k of a pilots license expense. I notice that getting a Private Pilot costs 10k but it doesn't seem possible to make any money. Commercial costs 100k it seems. I wasn't sure if there was like a Air Uber, where you could charter a plane or jet whenever, make 2-3k a flight, and essentially pay back that 100k over 30 to 40 flights or something opportunity like that. Someone else mentioned package delivery may be an option too?

@TonyDiNitto No, there's no such Uber-like company for flying. Even companies like Flytenow, which just facilitate ride-sharing (i.e. the pilots would still pay their share of the flight expenses) are considered "common carriers" by the FAA and get shut down because the pilots don't have commercial licenses. Even package delivery requires a commercial license. If you want to make any money at all as a pilot, you're going to need a commercial license.


text:
What's the difference between the "approaching minimums" and "plus hundred" callout for Boeing aircraft?
Is it essentially the same thing? And if so, does it vary based on the model of Boeing aircraft or airline's choice?

EGPWS callouts are selectable by customers, e.g. for Honeywell MK V and MK VII:

Mode 6 provides EGPWS advisory callouts based on the
menu-selected option established at installation (set by
program pin configuration). These callouts consist of
predefined Radio Altitude based voice callouts or tones and an
excessive bank angle advisory.

Among the choices:

“APPROACHING DECISION HEIGHT” or “PLUS HUNDRED” correspond to DH+100ft

“APPROACHING MINIMUMS” corresponds to DH+80ft.

Customers can also request specific callouts, e.g. DH+60ft (more).


text:
Why are turbine blades made thicker with great curvature and more streamline than compressor blades?
I can`t think it is about material limitations or aerodynamics

"I can`t think it is about material limitations or aerodynamics". It might actually be the main reason: compressor works with temperatures of some 300°C/500°F and speeds of some 500fts/150ms; turbine works with temperatures of some 1300°C/2000°F and speeds of some 1000fts/300ms. Compressor blades (or better, fan blades) are also taller than turbine blades so a higher curvature/twist makes sense for the former.

Indeed what sophit is saying seems correct. On smaller jet engines which do not have fancy stuff like active blade cooling, the turbine blades look quite similar to the compressor blades. Even the LP turbine blades on modern jet engines look quite similar to the compressor blades, with the exception of the outer ring, which is used to prevent interstage leakage of air, and is exclusive to turbines.

Also, there's often a single HPT stage driving upto a dozen HPC stages, so it makes sense that the single HPT stage is much more 'agressive' that the HPC stages, since the energy harnessed by the HPT equals the work done by the HPCs plus the losses.

First of all, let's begin with talking about axial compressors and axial turbines1). The short answer is that in both turbines and compressors, the blades are very much streamlined, just the flow regime is different (you can see e.g. the curvature & blade twist in the picture in the post Where can I find detailed dimensions of an aircraft engine compressor blade?)
The longer answer is...
Compressors

Low stage load: In a compressor, the problem is that pressure increases in flow direction, and that makes it very much more susceptible to flow detachment around the airfoil, which would lead to a stalling airfoil and subsequently to compressor stall. This limits the pressure ratio achievable per compressor stage, and hence leads to small turning.For the same reason, the target is to have the least flow obstruction possible to minimize flow acceleration (on the suction side).

Low flow obstruction: Additionally, less flow obstruction means more effective flow area and hence less throttling - more mass flow for a given size of the compressor (or a smaller compressor for a given design mass flow).

Both effects together lead to thin blades with low flow turning per blade (low stage load), and lots of compressor stages for the full compression ratio.
Turbines

High stage pressure ratio: In turbines stall is no problem because the pressure decreases along flow direction, so pressure ratios per stage can be high. Turbine stage pressure ratios are usually only limited to "below critical pressure ratio", in order to avoid high losses resulting from supersonic flow.

High flow turning is hence possible and advantageous, because you want high circumferential flow velocity (see Euler turbine equation) for high power per stage.

Blade thickness: Since the stagnation point on the leading edge shifts with changing velocity triangles, a large leading edge radius makes the blade better adapted to wide range of mass flows. Furthermore, a row of turbine blades is acting as nozzles to convert the pressure upstream to velocity downstream, so some obstruction/thickness is required.

so ..  turbine blades end up getting thicker.
The load difference between compressor stages and turbine stages can also be seen that gas turbines have about 4x more compressor stages than turbine stages  (eg GE 9HA: 14 compressor stages & 4 turbine stages)
While these are basic aerodynamic considerations, actual blade design is obviously becoming more of a trade-off, with mechanical properties, cooling design, and last not least manufacturability and associated manufacturing cost.
For more theory.. my favorite book on these topics is "Gas Turbine Theory" by Saravanamuttoo, Rogers, Cohen, Straznicky, and Nix.

1) For radial compressors & turbines the points are basically still valid, although less pronounced. In applications like automotive turbo chargers, cheap manufacturing becomes a significant driver compared to e.g. aerodynamic efficiency.


text:
Ice Protection System for supersonic aircraft
How does a supersonic transport aircraft IPS system work? Does it work only for the engine nacelle or both engine and wing. I was thinking only for nacelle since the wings are usually highly swept.
Also, how is it powered? through electrical system or air from engines? Are there any books I could refer to to find out more about systems of supersonic aircraft?
I am working on a project which has a theoretical supersonic business jet. Since there are no SSBJs, I would appreciate any help I could get.

There are no supersonic business jets.

@GdD The ones in the past, Tu-144 and Concorde, what kind of systems they had and why?

Those weren't business jets @itsChibi, they were commercial airliners, not private jets.

@GdD So the system configuration for supersonic jet would be different from supersonic airliner- because of size and weight difference?

Supersonic airliners are jets, are you asking how icing protection works on small as opposed to large supersonic airplanes? If not you need to clarify what you are asking.

Also, keep in mind that the Concorde  and TU-144 designs are from the 60s and the TU-144 wasn't very good, so they aren't good examples of how you would do it if you are designing an airplane now.

@GdD I am looking for systems information for supersonic business jets for a project. I was thinking of comparing it with other supersonic aircraft but I am not sure on what basis I should compare them to get near accurate results.

There, did that edit help?

@MichaelHall Thanks!

Depends on the aircraft. Concorde, for instance used electrical deicing system on its engine inlets, air data probes and wing leading edges to prevent ice accumulation during subsonic climb and descent.
https://www.heritageconcorde.com/concorde-ice-protection
Supersonic cruise typically takes place in the upper stratosphere and beyond, where no weather save only a few very powerful thunderstorms ever penetrates.  Secondly, deicing equipment would not be needed there as supersonic cruise typically causes a great deal of airframe heating due to atmospheric friction.  A Concorde cruising at Mach 2 typically had skin temperatures in excess of 150° F over its surface and the SR-71 encountered skin temperatures from several hundred to 1200° F over its airframe.  High supersonic and hypersonic aircraft would be even worse. Airframe icing will not form under these conditions.
Information on deicing systems on supersonic business jets (SSBJs) remains largely proprietary at this point, but I suspect they use similar schemes to that of the Concorde.  IF, that is, one of these designs finally goes on test flights (Ahem, Boom!) and stops with the CGI eye candy.

The several thousand degrees F on the SR-71 could only be found inside its engines - if at all. The outside reached around 600 F at stagnation lines and around 1200 F at the nozzle. Still enough to melt any ice.


text:
Are rotary engines the same as piston engines?
I’m researching into piston engine powered, propeller driven aircraft.
However, I’m really struggling to find manufacturers that make "piston engines".
For example, I came across Rotron, but it seems like they only make Rotary engines.
Are rotary engines the same as piston engines? If not, what manufacturers build piston engines for prop planes?

Welcome to the site. Your  question isn't very clear, and seems to be many questions in one. I've never heard of a rotar engine, do you mean a Wankel Rotary engine? If so, I suggest you do some research before you ask a question, and make the question applicable to aviation. You should also do research on aviation piston engines, there's a wealth of information on the web. Once you have a question which is clear and focused you can edit this question or open an new one.

@Engine lover, I believe that you ask about Rotax 503 engine on ultra lightweight aircraft design model by Quad City Challenger

I edited your question so it at least makes sense.  Please let me know if I captured your intended meaning correctly.

related:  https://aviation.stackexchange.com/questions/1256/what-are-the-differences-between-lycoming-and-continental-engine-designs

You are describing a Wankel type engine, which is not a piston engine, but is a type of 4 stroke "otto cycle" engine.
They have been around since forever (the 60s), and would seem to be ideal replacement for aircraft piston engines, having the simplicity and power to weight approaching that of a turbine.  You would think.
But if you read up on the Wankel's history with Mazda, and the numerous attempts to stick them in airplanes, you find they are just riddled with frustrating limitations:

High fuel consumption, like 2 strokes or worse (Mazda RX7s and 8s were notorious for lousy fuel economy).
Low torque production due to the very low "leverage" the combustion chamber is able to apply to the eccentric cam of the crankshaft. They are equivalent to an extremely short stroke piston engine.
Because of the low torque, they have to spin very fast to make any power, requiring very large gear reductions, although they don't suffer from the torsional resonance problems of gear reduced piston engines, because of the way the power strokes of multi-rotor Wankels overlap.
Apex seal wear, which Mazda finally dealt with by feeding oil directly to the Apex seals (equivalent to piston rings in a piston engine), which means they consume oil like 2 strokes.

There have been many attempts to make aircraft engines out of multi-rotor Mazdas, and they have flown, but eventually were abandoned due to technical problems (not to mention ear splitting noise levels - I saw an RX7 powered Van's RV-4 at Oshkosh in the 90s - wow what a racket it made, even with a muffler).
Roton is just another case of someone stumbling onto the configuration and making a go at getting around the engine's limitations. The configuration's simplicity and potential reliability is just so enticing.
However, there IS something new under the sun, with a new rotary design that just may be the answer.
As for propellers, oodles of propellers here.

I love rotary engines, but sad to say, everything you wrote here is correct.  They're an elegant and largely impractical power plant, with more in common with a multi-cylinder 2-stroke than with a 4-stroke piston engine.  They do have two major advantages: they run well on very low octane (the 1976 Cosmo 13B I owned called for 67 octane) and they're very light for liquid cooled engines (very competitive for power-to-weight even with a 2.5:1 gear or belt reduction system).  Fuel and oil consumption and emissions are what killed them, though.

When I was 16 an older brother's chum came to our house one day in his new '71 RX1.  It was a single rotor IIRC.  We were awestruck by the weird sound it made and it was reasonably quick by the standards of the day.   My high school math teacher in the early-mid 70s had an RX 3.  It was pretty fast.  But I dimly remember the engine was toast pretty quickly and he traded it in after only a couple of years.

The RX-1 was a 2-rotor 10A (1000 cc).  Mazda never sold a single rotor, though NSU, Suzuki, and Sachs did (not to mention the O.S. .30 Wankel model engine).  My Cosmo was scary fast -- would burn rubber in three gears, had throttle left at 110 mph in 4th (on a 5 speed), and would cruise from gas station to gas station at 90.  The slightest overheat would result in end plate warpage leading to coolant leaks, and it failed emissions every yet.

@ZeissIkon if you haven't seen the Liquid Piston rotary, you will probably get pretty excited.  I added a link to a video of it at the end of my post..

Cool video of a reconfigured rotary, but I wouldn't call it a "piston rotary".  It may have definite advantages, but I think they are trying to distinguish it with a misleading name.

I've heard of it, seen the animation videos.  I still see quenching issues (one cause of the poor emissions of the Mazda/Wankel rotary), and the fixed seals will have the same issues the rotor mounted ones did for Mazda, IMO.  There's little if any additional leverage over the Mazda/Wankel, so it'll still be a high speed, low torque engine.  And they're where NSU was in 1967 (while Mazda was already making important changes to the basic Felix Wankel design) -- still trying to translate patents into something roadworthy.  The only major improvements I see are compression and charge velocity.

I see the liquid piston's rotor has a hot end and a cold end as well -- that's going to cause problems.  Maybe their internal cooling fins will solve that, maybe they won't.  Mazda had fifty years trying to solve their problems.  These guys haven't even sold an engine yet, AFAIK.

The problems with Mazda's apex seals were in part related to the dynamic forces including centrifugal forces imposed by having them on the rotor.  Fixed seals are supposed to alleviate that.  My main question is is there still the sensitivity to warpage of the chamber walls.

@MichaelHall Liquid Piston is just the name of the company, intended to pique interest.  I would call the configuration a "radial rotary", since it is effectively a 3 cylinder radial as far as the forces acting on the crankshaft are concerned.  It's a radial whose single "piston" is able to visit each of the 3 "cylinders" in turn.  The thing is brilliant beyond belief.  Biggest problem is you are  stuck with that 3 cyl radial configuration and it may not be feasible to stack them like a multi-bank radial because of where the gases have to go.

Aaah, I read that as Liquid, Inc., Piston-Rotary Engine!  (incorrect grouping in my head...)  Thanks.

Although the Wankel engine is commonly called a rotary engine, in the early days of aviation, there was a rotary engine (which was a piston engine) that shared a lot of characteristics with a radial engine, with the biggest difference that the crankshaft was stationary and the crankcase turned. Here's more information:
https://en.m.wikipedia.org/wiki/Rotary_engine

pic source
Rotary piston engines are still manufactured. Wikipedia has the following to say about them:

A rotary engine is essentially a standard Otto cycle engine, with cylinders arranged radially around a central crankshaft just like a conventional radial engine, but instead of having a fixed cylinder block with rotating crankshaft, the crankshaft remains stationary and the entire cylinder block rotates around it.

The photo is from a company that makes replica's of Gnome engines, and this article mentions Le Rhône and Oberursel replica's being produced. Rotary piston engines are easy to find!

You win!  Great answer, and beautiful photo.  I had heard of these type of engines before, but it wasn't the first thing that came to mind.  And given the OP's command of English in the unedited first edition, I kinda don't think this is what they meant.  (if I had to guess they were visualizing an internal combustion reciprocating piston engine, with a rotating crankshaft)  I could be wrong, although I bet I'll never know because Engine Lover doesn't seem interested in responding to comments.

See JohnK’s answer for an explanation of rotary engines.
The best-known manufacturers of piston aircraft engines today are Lycoming, Continental and Rotax.


text:
How does a pilot communicate with ATC during a hijacking?
How does a pilot communicate with ATC during a hijacking?

Such information will reduce effectiveness of communication. If it is just for curiosity, I assume old reports may help to get an idea (and details will change from time to time), there were various hidden ways -- Large terrorist organizations know the answer, but a lot of hijacking happens from desperate (or drunk) people (not all planes depart from international airports and/or western countries, not all are the big planes)

They set their transponder to 7500, which signifies a hijacking is talking place. ATC would then likely communicate with police etc.


text:
What is the meaning of (HR) (LY) (FOR) in radio phraseology?
Need help!
Can’f figure out what’s the meaning of (HR) (LY) (FOR) beside some words from this document:  Source.

source document: https://files.fpz.hr/Djelatnici/ifrancetic/Radiotelephony-communications-1-handbook.pdf

@tedder42, good on ya for finding the source, saved the OP a possible DV and multiple questions!  Anyway, I put a link in the question itself...

"LY" and "FOR" are simply optional suffixes. In other words, "immediate" can be "immediately".
"HR" can only be determined from inference: this is a Croatian document, "HR" is the country code for Croatia (Hrvatska).

More explicitly, the (HR) entries appear to be local additions (or non-exclusions) that are not found in ICAO 10/II/5.2.1.5.8

they aren't all italicized, eg airborne, read.

No, they're not all italicized.   But checking against the ICAO document, none of the (HR) entries are listed (including Airborne and Read).


text:
Minimum Sink Rate in Sailplane
How do gliders ascend (either with an engine or thermal) at best rate of climb if it is very close to stall? Or they move up by sacrificing that best Rate of Climb. In image the best CL^3/CD is Minimum power required.

Can you clarify what the question is?

Glider (sailpane) pilots frequently thermal at "close" to the stall speed.  Given the slow speed and high angle of bank, spins are a real risk if the aircraft is capable of spinning.  This is one reason spin recovery - in the UK at least - is part of a glier pilot's annual check.

Usually, the designers make sure that the margin between the minimum sink speed and stall speed is larger. Take a look at a real example: the flight polar of the ASK21, one of the most common glider trainers.

The lowest sink speed when the glider is fully loaded (G/S is the wing loading) is marked with "ger. Sinken", and at 82km/h it is about 15km/h (+22%) larger than the stall speed (~67km/h). In gusty weather the pilots will fly at higher speeds, trading off performance against safety.
On a more general note, assuming constant zero-lift drag and parabolic induced drag, the mathematical equation to calculate the factor between the stall speed $V_S$ and the minimum sink speed $V_{\textrm{min sink}}$ would be the following one:
$\frac{V_{\textrm{min sink}}}{V_S} = \sqrt{\frac{C_{L,max}\cdot k}{C_{D0}}} = \sqrt{\frac{C_{L,max}}{3\pi \cdot C_{D0} \cdot AR \cdot \epsilon}}$
$C_{L,max}$ is the maximum lift coefficient attainable by your airplane,
$C_{D0}$ the zero lift drag, and
k the factor used for the quadratic term in the drag coefficient equation ($C_D = C_{D0} + k\cdot C_L^2$, which depends mainly on the aspect ratio AR of the wing and the oswald factor $\epsilon$)

This is not really intentionally - the increase in sink rate close to stall is the result of growing flow separation. Without that, sink speed would decrease right up until stall.

How do gliders ascend at best rate of climb?

They do it by closely watching speed and stick forces.
You are right, when aspect ratio is high, the polar point of minimum sink is at a very high lift coefficient. If we use the parabolic drag equation, minimum sink c$_\text{L}$ over aspect ratio looks like this:
$$c_L = \sqrt{3\cdot c_{D0}\cdot\pi\cdot AR \cdot\epsilon}$$
With a minimum zero-lift drag coefficient of 0.008 and Oswald factor $\epsilon$ = 0.98 we get
 Aspect  | minimum sink rate at
 ratio   | lift coefficient:
--------------------------------
   15    |   1.053
   20    |   1.216
   25    |   1.359
   30    |   1.489

With a standard-class glider the last polar point is probably not flyable at all. Flaps not only help to shift the laminar bucket up and down, but also allow high-performance designs to actually fly at their optimum polar points.
When thermalling I pay close attention to stick forces and have tried out stalling the glider before. Every type behaves differently, so I recommend to gain some altitude when flying a new type and then stalling it several times, with a variety of bank angles. In most cases control forces in roll become really low and some even will show stick forces into the circle right at stall. Depending on the airfoil on the outer wing, in that case you quickly pitch down a bit or throw the stick to the other side to support the stalling wing.
In sailing when you are close to the wind you should always play a bit with the rudder and watch the leech of the sail. If it starts to flutter, let go a bit on the rudder and then slowly tighten it again.
The same should be done when thermalling. When you know your plane, this will soon become second nature. Especially the most modern gliders can happily be flown down to very low speeds, but then their sink rate goes up because a lot of the wing has already separated airflow. Here it is better to fly at a faster speed: Controls are stiffer, control response is better and you circle at the same speed as everyone else in that thermal.
With weak and blue thermals (no clouds) you need to fly very tight circles because then thermals are narrow and climbing is only possible at steep bank and low speed. But this is hard work - most pilots fly for fun and happily accept a slightly lower climb rate but can fly at a lower bank angle and without paying close attention to speed at every moment.

It’s worth clarifying that ‘what would give the minimum sink rate in static air’ is not the only, and not the most important factor that pilots take into account.  Typically the pilot will try to spend a high proportion of their time in the areas of strongest lift.  While the AoA might affect the glider’s performance by a few tens of feet per minute, staying in a strong thermal core can gain several hundred fpm in a climb.

@Frog Yes - and where is the updraft strongest? At its center, which can be rather narrow. Which in turn requires tight circles. At high lift coefficients. If it weren't, gliders would mostly fly straight.

either with an engine or thermal?

Well, with an engine the best rate of climb is Vy.  Lower angle of climb than Vx but faster.  This results in a higher rate of climb.
With a thermal we use V min sinken because the rate of ascent is thermal updraft speed - sinken rate.
At V min sink the aircraft has a steeper angle of descent towards earth but a slower airspeed, resulting in a slower rate of descent.
This enables the updraft to increase altitude as much as possible, with the added benefit of slower airspeed allowing tighter turn radii to stay in the thermal.
Notice soaring birds, such as eagles, have broad, heavily cambered wings, with slatted tips, to fly as slowly as possible in thermals.